1. Field of the Invention
This invention relates to a method of making print head assemblies and to print head assemblies.
2. Brief Description of the Prior Art
Various embodiments of a prior art print head assembly are disclosed in U.S. Pat. No. 3,968,745 to Paul H. Hamisch, Jr. granted July 13, 1976. One embodiment has a single mounting block with a concave mounting surface for mounting drive wheels and support means. Printing bands are trained about the drive wheels and the support means. The mounting block is formed integrally with the support means and one side plate. There is a second side plate connected to the mounting block and a selector for engaging any drive wheel in its central hole to advance any selected printing band. The selector extends through an opening in the second side plate. The selector is assemblied onto the side plate before the second side plate is connected to the mounting block. In another embodiment suited for multi-line printing there are two such mounting blocks, two series of drive wheels and two series of printing bands and an integral side plate. There is a second side plate connected to the mounting blocks and there is a selector for each series of wheels. The print head assembly is assembled similarly to the manner described with respect to the previously mentioned embodiment.
In applicant's prior art print head assembly according to U.S. Pat. No. 3,968,745, one of the side plates is molded integrally with the mounting block and the parting line is taken along that side plate. This requires the mold for the mounting block and the integral support means to be provided with a certain draft angle from side-to-side to enable the resultant molded structure to be removed from the mold. Moreover, the molding of the side plate integrally with the mounting block and support means has at times caused the resultant structure to be warped.
The goal of high quality printing may not be achieved when the print head components are warped or when molding draft is other than negligible. High quality printing is required when printing machine readable codes such as the OCR code or various types of bar codes.
U.S. Pat. No. 3,796,152 to Eugene W. Finke and Paul H. Hamisch, Jr. granted Mar. 12, 1974 discloses a print head assembly having a mounting block with side plates. The side plates mount the shaft which in turn mounts the multisided side-by-side wheels.